The power output of an internal combustion engine is determined by many factors. One important factor is the energy content of the fuel being consumed by the engine. For a given set of operating conditions, as the energy content of the fuel, typically measured in BTUs, is decreased, so the power generated by the engine decreases. For an engine operating under a given load, this reduction in power output will translate into a reduction in the speed of the engine. In order to return the power output of the engine to the desired level, it is possible to increase the supply of fuel and air to the engine. However, once the fuel/air mixture is being supplied at the maximum rate for the engine, further increases in power output cannot be achieved in this way.
One situation in which this problem arises is in the case of an internal combustion engine burning gaseous hydrocarbons as a fuel, for example at an oil well head. Internal combustion engines are used at well heads, for example, to generate electrical power and drive production equipment. Preferred engines for this operation are those capable of using gaseous hydrocarbons, such as natural gas, as a fuel. It would be highly advantageous if such engines could be powered using gaseous hydrocarbons produced from the well, such as associated gas and gas produced as a result of secondary oil recovery techniques. However, such gases generally have a very low energy content, often containing considerable quantities of carbon dioxide. This is particularly the case with gas produced by secondary oil recovery, which entails injecting carbon dioxide into the well to enhance oil production. The carbon dioxide thus injected is subsequently produced along with the gaseous hydrocarbon fractions, thereby reducing the energy content of the gas and its quality as a fuel.
Operating an internal combustion engine using such low quality fuels as associated gas and gas produced as a result of secondary recovery techniques severely limits the power output available from the engine. As discussed above, once the maximum supply rate of gas to the inlet of the engine has been reached, it is not possible to obtain further increases in power output. This represents a serious restriction in the duties to which the engine can be applied.
Accordingly, there is a need to be able to use low quality fuels, such as associated gas and gas produced as a result of secondary oil recovery, as fuels for internal combustion engines without the heretofore encountered problems of restricting the power output obtainable from the engine.